Method of casting rigid foam to support a hollow flexible plastic shell

ABSTRACT

PROCESS FOR PREPARING RIGID, IMPACT-RESISTANT ARTICLE COMPRISING A HOLLOW OUTER SHELL COMPONENT AND AN INNER RIGIDIFIER COMPONENT COMPRISING A CELLULAR PLASTICS MATERIAL. THE ARTICLE IS FORMED BY MOLDING THE HOLLOW FLEXIBLE SHELL COMPONENT, REMOVING THE MOLDED SHELL COMPONENT FROM ITS MOLD, INTRODUCING A FOAMABLE ORGANIC PLASTIC INTO THE SHELL AND ALLOWING IT TO FOAM AND SOLIDIFY INTO A RIGID   FOAM IN CONTACT WITH THE ENTIRE INNER SURFACE OF THE FLEXIBLE SHELL.

NOV. 1972 A. H. ROBERTS METHOD OF CASTING RIGID FOAM TO SUPPORT A HOLLOWFLEXIBLE PLASTIC SHELL Original Filed Jan. 28, 1966 INVENTOR LARTHURH.-ROBERTS o o ro 0 MM 0 y 7 kmmmmm 5 United States Patent OficePatented Nov. 21, 1972 3,703,571 METHOD OF CASTING RIGID FOAM TO SUPPORTA HOLLOW FLEXIBLE PLASTIC SHELL Arthur H. Roberts, 12 Lynnwood Drive,Westbury, N.Y. 11590 Continuation of abandoned application Ser. No.760,415, Sept. 18, 1968, which is a division of application Ser. No.523,778, Jan. 28, 1966, now Patent No. 3,419,455, which is acontinuation-in-part of applications Ser. No. 455,764, May 14, 1965, nowPatent No. 3,405,026, and Ser. No. 475,989, July 30, 1965, now PatentNo. 3,414,456, which in turn are continuations-in-part of abandonedapplication Ser. No. 22,002, Apr. 13, 1960. This application May 10,1971, Ser. No. 142,037

Int. Cl. B29d 27/04 US. Cl. 26445 21 Claims ABSTRACT OF THE DISCLOSUREProcess for preparing rigid, impact-resistant article comprising ahollow outer shell component and an inner rigidifier componentcomprising a cellular plastics material. The article is formed bymolding the hollow flexible shell component, removing the molded shellcomponent from its mold, introducing a foamable organic plastic into theshell and allowing it to foam and solidify into a rigid foam in contactwith the entire inner surface of the flexible shell.

RELATED APPLICATIONS This application is a continuation of applicationSer. No. 760,415, filed Sept. 18, 1968 and now abandoned which was adivision of application Ser. No. 523,778, filed Jan. 28, 1966, now Pat.3,419,455, which is continuation-in-part of applications Ser. Nos.455,764, filed May 14, 1965, now Pat. 3,405,026 and 475,989, filed July30, 1965 now Pat. 3,414,456, which, in turn, are continuation-in-partapplications of application Ser. Nos. 22,002, filed Apr. 13, 1960.Application No. 22,002 has been abandoned.

This invention relates to a process for preparing novel, rigid, impactresistant articles. The articles are of varying sizes, may have more orless intricate shapes and may have undercuts. Similar articles in theprior art were made predominantly of ceramic or plaster materials. Theseprior art articles of manufacture have the disadvantage of being fragileand easily chipped. They require much hand finishing on the seam linescaused by the mold seams.

The prior art has also disclosed various casting processes formanufacturing seamless hollow articles out of plastisols and similarplastics materials. The resulting product is quite attractive and can bedecorated as easily as plaster, and in fact more easily than ceramics.The plastisol articles so cast will not chip, however they aredeformable. Also, if the die is seamless, a seamless product can beobtained. Plastisol has a defect called creep or cold flow, whichresults in a warpage or distortion at somewhat higher than ambienttemperatures as in the vicinity of household radiators and electriclamps. This property is generally characterized by the temperature atwhich distortion occurs.

Therefore, manufacturers of such prior art articles as lamp bases havehad the choice of producing ceramic and plaster articles or the likewhich are resistant to heat but fragile, or producing plastisol articleswhich have good impact and chipping resistance at normal temperatures,but which are deformable, have cold How and poor impact resistance atlow temperatures. The phenomenon of cold fiow has also been called heatdistortion.

An object of this invention is to provide manufactured articles withimproved properties and without the disadvantages of the prior artarticles.

A further object is to provide a process for producing small and largeseamless objects of plastics with improved resistance to cold flow,chipping and breakage, and which is distinctly superior to prior artprocesses and the products produced thereby.

Other objects of this invention will become apparent from thedescription of this invention further below.

The articles of manufacture of my parent applications are rigid,three-dimensional and hollow. They comprise two components: (1) an outerlayer component, also called the shell and (2) an inner layer component,also called the flesh or rigidifier. In most of the cases varyingparallel cross sections of a single article show varying dimensions andshapes or configurations, indicating curved sidewalls and undercuts. Inother cases the cross sections may be identical, indicating box-shapedor cylindrical objects. In an alternative form of said parentapplications the outer layer component and inner layer component jointlyform a cavity and this cavity is then filled with a reinforcing spine,such as a rigid plastics foam material. The outer layer component ismade of a flexible plastics material, illustrated by plastisol andpolyethylene, whereas the inner layer component in the various parentapplications is illustrated for instance by asphalt, plaster of parisand a composition comprising a filler which is bonded by the elastomersolids of a latex.

In contrast to the inventions of the parent applications the compositearticles of manufacture of the instant invention comprise a hollow outershell component and an inner rigidifier component. Further, the outershell component is a premolded pliable plastics and has an accessopening. The pliable or flexible nature of the premolded hollow outershell component is characterized by the fact that, when free of therigidifier component, it can be deformed, at least temporarily, by theapplication of hand pressure. In my parent applications the term skinwas used to designate the shell component. The latter expression ispreferred. The inner rigidifier component is a rigid cellular plastics.The rigidier component is positioned within the space enclosed by theouter shell component and the former is in intimate contact with theentire inner surface of the latter. The rigid cellular plastics may alsobe called rigid plastics foams and may have either a closed cell or anopen cell structure. The closed cell structure is preferred.

The composite articles of manufacture of the instant invention arerigid. In this context the term rigid means a radical increase inrigidity when compared with the outer shell component itself and it alsoindicates utility for purposes requiring at least a certain degree ofrigidity.

The rigid cellular plastics composition according to this invention actsas a rigidifier for the outer shell component. The premolded outer shellcomponent is hollow and the inner rigidifier component may fill thecavity formed by the hollow premolded shell component fully or in part.In the latter case the outer shell and inner rigidifier componentsjointly form a cavity and in such cases a reinforcing spine componentmay be present on the inner surface of the joint cavity. This will bediscussed further below in greater detail.

The varying parallel cross-sections of a single composite article ofmanufacture of this invention may show varying shapes and dimensions,indicating curved sidewalls, angulated sidewalls and undercuts, or mayshow identical shapes and dimensions, indicating box-shaped orcylindrical objects.

The shell is preset in its shape by a molding or forming operation. Itis formed from a plastics material, which is preferably pliable andresilient. Depending on the plastics material selected to form theshell, the molding operations may vary, in order to utilize the mostadvantageous method for the selected plastics. The outer surface of theshell readily receives coloring materials for decorating the compositearticle. In some cases, such as when the shell is of polyethylene, theouter surface may be pretreated prior to decoration. The inner walls ofthe shell define an internal cavity accessible through an opening in theshell. The inner rigidifier component is in intimate contact with theinner walls of the preset shell and is in supporting relationship to theouter shell. This inner component acts as a rigidifier and rigidlymaintains the outer shell in its preset shape. The inner rigidifier isformed by a rigid plastics foam and is described in detail furtherbelow. The rigid foam composition is preferably applied in a liquidstate and solidifies Within the preset shell. In a preferred embodimentthe shell component acts as a mold in which to form the inner rigidifiercomponent. Depending on the properties of the shell and the rigid foamcomposition, the setting of the latter may be performed while the shellis in a second mold or die. This second mold or die would usually be asplit mold and is used to prevent deformation of the shell during thecasting and setting of the rigid foam composition forming the innerrigidifier component. The latter acts as a structural rigid backingmember. The use of a second mold is superfluous in many cases.

The outer shell component of the composite article of manufacture ofthis invention has a preferred wall thickness of about inch to about Ain thousand-ths of an inch, this corresponds to a range of from about15.625 mils to about 250 mils. The lower figure may be rounded out toabout 15 /2 mils. The inner rigidifier flesh component may have a wallthickness of that equal to the thickness of the shell, or even be as lowas one-half of the thickness of the shell, and in many cases the innerrigidifier fills the cavity formed by the outer layer in full. Byvarying the formulation of the rigid foam composition, a tougher or morerigid inner rigidifier would permit the use of a thinner layer than aless tough or less rigid inner rigidifier, while maintaining thecomposition of the shell constant. By changing the density of the rigidplastics foam it is possible to change its rigidifying action. A moredense rigid foam is more rigid than a less dense rigid foam, assumingthat otherwise both have the same composition.

In one of the embodiments of this invention the outer shell and innerrigidifier jointly form a second cavity and a reinforcing spine may beapplied as a third component in the entirety or in part of the secondcavity. Such a spine assists the rigidifying action of the inner layerand toughens the composite article of manufacture. In this applicationthe expression ancillary reinforcing element is preferred to theexpression spine.

As stated above, the cellular plastics of this invention may be of opencell or closed cell structure. Most rigid foams are closed cellstructures. Open cell rigid foam structures can be prepared fromurea-formaldehye and phenol-formaldehyde foaming compositions. Rigidpolyurethane foams with open cell structures can be prepared by the useof special silicone surfactants as additives, designed for thisparticular purpose.

When considering the improvement which the composite articles ofmanufacture of this invention show, versus either the properties of theshell component or of the rigidifier component, utility for manypurposes becomes apparent. In case of a lamp base resistance todeformation is achieved. Such deformation may be caused by compressiveforces resulting from the assembly of the lamp. The resistance to impactalso increases. The thermal deformation is also decreased. The lattereffect is important in manufacturing planters. These have to withstandwarm climates and sub-tropical or tropical temperatures withoutdeformation. In preparing wash basins the resistance to hot and coldwater is improved and achieved.

inch. Expressed The rigidifier may contribute thermal insulation inaddition to rigidifying the end product. While preventing the bucklingand deformation of the shell component the impact resistance andresistance to chipping of the rigidifier component are also improved.These properties indicate utility for a great many composite articles ofmanufacture. All the shell components used herein have an accessopening. 'In most cases the surface area of the access opening, whencompared with the total external surface area of the shell, is small. Inother cases it may be larger. For many products prepared according tothis invention the surface area of the access opening does not exceedone-sixth of the total external surface area of the shell component. Asan illustration it may be mentioned that a hollow cube having one sideopen as access opening has an access surface area of one-sixth of thetotal surface area of the cube.

THE OUTER SHELL COMPONENT Plastisols illustrate an eminently suitablematerial to form the shell portion of the articles of manufacture ofthis invention. Plastisols are well described in the literature, as e.g.in Modern Plastics 26, 78 (April 1949) by Perrone and Neuwirth. They aredispersions of finely divided polyvinyl resin powders in liquid organicplasticizers. The resins contain predominantly polyvinyl chloride withor without some other polymerized monomer. They are polymerized to adegree where they have very low solubility at room temperature.Therefore, instead of dissolving them, the plastisols contain the resinsin a dispersed state; the dispersions are usually of creamy consistencyat room temperature and are always fluid to a certain degree. A greatvariety of plasticizers can be used. Dioctyl phthalate is an example.Dioctyl adipate is another example, which frequently is used inadmixture with dioctyl phthalate. Polyester plasticizers are also wellknown. The plastisols usually contain a stabilizer and may containpigment, if so desired. For convenience and to achieve brevity, a fewpublications may be referred to, which all deal with plastisols, theirformulation and application methods: (a) Geon Resin 121 in PlastisolCompounding. Service Bulletin PR4, revised October 1958, B. F. GoodrichChemical Company. 24 pages. (1)) The Vanderbilt News, vol. 26, No. 3,June 1960. R. T. Vanderbilt Company, Inc., page 12. (c) Modern PlasticsEncyclopedia Issue for 1961, published in September 1960. Vinyl polymersand copolymers. Pages 129 to 132. Plastisol Molding, pages 765 to 771.(d) Modern Plastics Encyclopedia 1965 (issued 1964). Vinyl Polyggeorsand Copolymers, page 271. Plastisol Molding, page Recently a reactivevinyl plastisol system Was introduced on the market. This consists of amixture of a vinyl dispersion resin and a reactive monomer. The formeris dispersed in the latter. When heat is applied to this system, alsoused to cause gelation and fusion, the reactive monomer polymerizes andproduces a more rigid product than previously produced with conventionalplastisols. Reactive acrylic monomers illustrate examples of suchreactive monomers.

When molding plastisols, the material is heated to a gelling temperatureand a gelled film or layer is formed which is very weak and cheesy, butwhich does not flow. Further heating is required to fuse the deposit,causing the resin to dissolve in the plasticizer and form a toughhomogeneous resinous mass in which the powdered resin and liquidplasticizer have formed a single uniform phase. The fusion transformsthe cheesy deposit or film to a tough leather-like homogeneous shell.

With regard to temperatures required, these are well known in the art.They vary from composition to composition. They vary with time. Thereare, further, three types of temperatures involved: (1) oven temperature(2) mold (die) temperature and (3) temperature of the plastisol.Gelation temperature may be accomplished by heating the oven from 150 to600 F. and usually is between a plastisol temperature of 150 to 300 F.The necessary times vary with the temperature used. Fusion isaccomplished by heating the gelled layer in ovens from about 350 F. toabout 650 F. The achieved plastisol temperature for fusion shouldadvantageously range from about 350 to 450 F. The gelation temperatureand fusion temperature depend on the formulation of the plastisols.Therefore some divergence from the above temperature ranges may occur ifspecial formulations are prepared.

The most useful molding methods for plastisol shells are illustrated by(a) slush molding, also called slush casting and (b) rotational molding,also called rotational casting. The expression casting is used becausethe plastisols are applied in fluid state and for this reason theoperation has similarity to metallurgical casting. Seamless dies arepreferred for the intermediate products of this invention. They can bereadily utilized, even when complicated undercuts exist in the dies, asthe shells produced from H the plastisols are flexible, elastic and havea shape memory, i.e., they recover from their stretched position,obtained during removal, to the original molded shape.

When slush molding or slush casting is used, in the first step an excessof plastisol may be poured into the seamless die. As the plastisolreaches gelation temperature, the layer adjacent to the metal wall ofthe mold gels, i.e., solidifies. The thickness of the gelled wall isdetermined by the duration of time the mold is exposed to thetemperature of gelation. The excess plastisol is then removed by pouringoff the liquid portion. Heating is then continued to complete the fusionand the molded shell is then removed or stripped from the mold. Thereare two methods known in slush molding: (i) One Pour Method, and (ii)Two Pour Method. Both are well known in the art and are applicable tomake the shells of this invention from plastisols.

Rotational molding is another method of casting. The basic departurefrom slush molding is that, instead of an excess of the liquidplastisol, a premeasured quantity of the fluid is used when charging themold. This eliminates the need for removing any excess. As the moldcontaining the charged fluid plastisol is rotated on the rotationalmolding machine and the mold is heated, gelation of the plastisol occursuniformly on the inner surface of the heated mold. By continuing theheating and/or increasing the temperature of the mold, the gelledplastisol fuses. The fusion completes the molding of the shell and the'completed shell is then stripped and removed from the mold.

Whereas the casting by slush molding or rotational r molding ispreferred to form the shell from plastisols, other methods known in theart may also be followed to achieve the same purpose. Objects made ofplastisols frequently display the defect known as cold flow. Cold flowmay be defined as the warpage or flow of material caused by its normalenvironmental temperature. Cold flow in plastics is analogous to thewarping of a wax candle in a hot climate, and when a thermoplasticproduct is subjected to compression, tension or flexing, the cold flowcharacteristics become even more accentuated. When a condition oflocalized intensified heat, such as that to which lamp bases are oftensubjected, is imposed upon a stressed article, cold flow warpage becomescritical and often results in making further use of the articleimpossible. The application of a rigidifier in accordance with thepresent invention counteracts the cold flow characteristics of plastisolshells, or at least reduces them to commercially acceptable limits.

Considering the aim of this invention of producing rigid articles theflexible nature of the plastisol shells is a drawback. The applicationof the rigidifier component rectifies this defect.

Polyolefins, such as polyethylene and polypropylene are otherillustrative examples for the production of the shell portion of thisinvention. Polyethylene is made today of varying properties with the lowpressure and high pressure polymerization processes. It is supplied withvarying densities, molecular weights, flexibility and othercharacteristics. The types of polyethylene most suitable for thisinvention are pliable, flexible and show some degree of elasticity.Polyethylene is preferred in this invention over polypropylene since itis more easily formed into pliable and flexible shells. Polyethylenecopolymers, such as ethylene-vinyl acetate and ethylene-ethyl acrylatecopolymers, offer improved flexibility and resilience. They arerubber-like and similar to elaston'leric plastics. For the production ofshells from polyethylene and polypropylene seamless dies are notsatisfactory and two-piece dies are preferred, using blow molding orother methods. Polyallomers belong to this class of materials, as theyare copolymers of ethylene and propylene.

The shell portion of the articles of manufacture of this invention maybe formed of other materials such as vulcanized natural rubber orsynthetic rubber. The shells may be formed according to known proceduresof rubber technology. One of the methods useful in preparing shells fromrubber is to use latex molding (latex casting) compounds, utilizingplaster of paris molds. The Vanderbilt News, vol. 27, No. 4, December1961, page 72, deals with latex compounding which can be used to makeshells for articles according to the present invention.

Other suitable plastics materials, which can form the outer layer shellsof this invention are illustrated by methyl methacrylate polymer, ethylcellulose, polycarbonates, polyurethane elastomers, flexible epoxycompounds, fiexible polyesters, amongst others. Some illustrativeexamples are given below:

EXAMPLE A Methyl methacrylate All percentages in this example and inthis specification are weight percentages. A mixture was prepared of62.5% methyl methacrylate monomer, 0.6% benzoyl peroxide, 2.1% whitecolor paste concentrate, compatible with methyl methacrylate, 34.3%polymethylmethacrylate, Du Ponts Lucite 30, 0.5% dimethyl-p-toluidine,totaling The shells were prepared by casting into suitable molds. Thecomposition of this example polymerizes at room temperature. Heating to100120 F. accelerates polymerization considerably. Latex molds can beused. Plaster and clay molds may also be used, if coated with gelatin,cellulose acetate, sodium silicate or tin foil. Casting was carried outin a latex mold in 3 subsequent coats and yielded a molded shell withacceptable flexibility and adequate mold surface reproduction.Plasticizers may be incorporated, if desired. Harflex 340 of HarchemDivision, Wallace & Tiernan, Inc. is a suitable resinous-type, primary,non-migratin g, saturated polyester plasticizer, compatible with methylmethacrylate monomer. The color paste was used to stain the shell. Itsuse is optional.

EXAMPLE B Polycarbonate Polycarbonates can be cast from organic solventsolutions. Polycarbonates dissolve, with ease e.g. in methylenechloride. A solution was prepared from Lexan No. (General Electric Co.)powder to form a solution of 83.3% polycarbonate in 16.7% methylenechloride, yielding 100% of the solution. -As an example, this solutioncan be slush cast in latex molds, and air can be blown in to assist involatilizing the solvent. The latex molds are standard in castingplaster of paris objects. The polycarbonate shell remains in the mold.It is very strong, flexible and durable, and can easily be stripped fromthe mold. To reduce the effect of shrinkage, fillers may beincorporated. A ratio of equal weights of filler to polycarbonate is anillustrative example. The resultingshell is still strong. Polycarbonateresins are marketed by General Electric under the trade name of Lexan.Polycarbonates can be described as polymeric combinations ofbi-functional phenols or bisphenols, linked together through a carbonatelinkage. They can also be blow molded and vacuum formed.

EXAMPLE C Flexible epoxy resin The proper composition has at least threeingredients. (I) a low molecular weight epoxy resin of theepichlorhydrin-bisphenol Acondensation product type, like ShellChemicals Epon 828. (Epon is a registered trademark of Shell); (2) lowviscosity liquid aliphatic polyepoxides, like Epon Resin 871, whichimparts increased flexibility to Epon resin compositions; and (3) acuring agent, illustrated by diethylenetriamine andtriethylenetetramine, respectively known as DTA and TETA. Othercomparative items, known in the trade, may be replaced for thecommercial products mentioned. Fillers may be present as additionalingredients. A suitable additive to regulate viscosity is asubmicroscopic pyrogenic silica prepared in a hot gaseous environment,marketed by Cabot Corporation under the trade name of Cab-O-Sil. Asatisfactory composition to obtain shells is 44.25% Epon Resin 828,44.25% Epon Resin 871, 2.65% of Cab-O-Sil and 8.85% diethylenetriamine,totaling 100%. This composition sets at room temperature in about 5hours and at 80 C. it sets in 2 hours. The composition may be variedaccording to principles known in the art. Shells can be premolded inlatex molds or other elastomer molds. These are actually multi-piecedplaster of paris molds externally reinforcing an entirely separatesecond flexible elastomer mold, having one opening for pouring in thecomposition to be molded and set. The rubber surface is coated with aparting agent and the epoxy composition is slush cast into the molds.The slit mold here described is used to mold shells showing undercuts.Other molds and molding methods can also be used, depending on thearticle to be manufactured. Epoxy plasticizers include epoxy compoundsof fatty oils and their acids. Epoxy novolac resins and cycloaliphaticepoxies are other illustrative members of this group. Polyamids and acidanhydrides may also be used as curing agents.

EXAMPLE D Flexible polyesters Polyester resins are usually made in twosteps. In the first step a condensation reaction is carried out betweena dibasic acid and a diol and this is then blended with a monomer.Maleic anhydride and fumaric acid are examples of the dibasic acids.Other unsaturated acids could also be used, like itaconic. Phthalicanhydride and isophthalic acid may be part components of the acids, tosecure desired modifications. The useful glycols form a long list knownin the art. Propylene glycol, ethylene glycol, diethylene glycol anddipropylene glycol are illustrative examples. Neopentyl glycol isanother example.

Styrene is most frequently used as the crosslinking monomer. Vinyltoluene is another example. Laminac Polyester Resin EPX-l263 is aflexible polyester resin containing styrene monomer. Laminac is aregistered trademark of American Cyanamid. A composition was preparedfrom Laminac Polyester Resin EPX1263 92.6%, MEK peroxide 2.7%, CobaltNaphthenate solution (6% Co) 0.27%, Laminac Additive #10, 1.73% andCab-O-Sil 2.7%, totaling 100%. MEK peroxide is methylethyl ketoneperoxide. Laminac Additive #10 is a petroleum wax composition dispersedin styrene, for ease of incorporation into polyesters. It improvessurface characteristics. The peroxide is the crosslinking agent and thecobalt assists the crosslinking. Flexible polyesters usually containlong chain acids or glycols. The gel time at room temperature is about10 minutes for this composition. The Cab-O- Sil assists in regulatingthe thickness of the deposit if slush casting is used for molding. Twoor three coats can be slashed to obtain a desired shell thickness. Theshell formation occurs at room temperature. More rigid polyesters can beblended with the flexible one used in this example, to vary properties.Latex molds and those utilized for epoxy resins, may be used withpolyesters.

EXAMPLE E Isocyanate elastomers (urethane elastomers) Liquid urethanepolymers, such as DuPonts Adiprene L-lOO, can be transformed into tough,rubbery solids by reaction of the isocyanate group with polyamine orpolyol compounds. In addition, some materials which do not containactive hydrogens, such as the titanate esters, appear to catalyzecross-linking. Adiprene L-l00 can be cured with diamines, or moisture(water), or polyols, or by catalysts, such as lead or cobaltnaphthenate, potassium acetate and titanate esters. Tetrabutyltitanateis an example of the esters. One of the popular polyamines is MOCA,which is 4,4'-methylene-bis-(2-chloroaniline). A formulation isillustrated by 100 parts of Adiprene L-100 and 12.5 parts of MOCA, whichgives a MOCA percentequivalent of 95. Parts are by weight. Conditionswere: Mixing temperature: 212 F, cure temperature: 212 F., curing time:3 hours. LD420 is a different type of liquid urethane elastomer, whichyields high quality vulcanizates when cured with MOCA. A respectiveformulation is illustrated by 100 weight parts of LD-420 (DuPont) and8.8 weight parts of MOCA. This is mixed and cured the same way asAdiprene L-100, for the same length of time. It is improved byaftercuring 1 week at 75 F. at 60% relative humidity. In making a shellrotational molding is recommended both for Adiprene L-lOO and forLD-420. A silicone mold release is advantageously used to assistseparation from the molds.

EXAMPLE F Ethyl cellulose Ethyl cellulose shells can be molded by vacuumforming and injection molding, amongst other methods. The same appliesto cellulose acetate and cellulose acetobutyrate. Combination of castingand hot melt methods may also be used.

The preset molded outer shell components can be prepared by variousmolding processes. The selected process depends on the selected plasticmaterial and on the shape and size of the shell to be molded. Forillustrative purposes a few examples are given. Casting such as slushcasting or rotational casting: Plastisol, flexible polyester, flexibleepoxy resins, methyl methacrylate, polycarbonates from solution, rubberfrom latex, etc. Injection molding or extrusion: plastisol,polycarbonates, ethyl cellulose, polyethylene, cellulose acetate,cellulose acetobutyrate, etc. Vacuum forming: polyethylene,polycarbonates, polyallomers, etc. Blow molding: polycarbonates,polyethylene, polyallomers, ethyl cellulose, cellulose acetate, etc. Hotmelt process: ethyl cellulose, plastisol or other plasticized polyvinylchloride composition, polyethylene, etc.

Whether a one-piece, two-piece or multi-piece mold is required, ,dependson the selected shell material and, to some extent on the shape of themanufactured article. The molding process also influences the moldselection. Plas' tisol illustrates a shell forming material whichpermits the use of one-piece molds even if the shell has many undercutsin its shape.

Methyl methacrylate illustrates a material which requires at leasttwo-piece molds in many instances. Blow molding and vacuum forming areusually carried out in two-piece or multi-piece molds. One-piece moldsform seamless molded shapes. Two-piece molds cause, in most cases, someseam formation. It may be necessary to eliminate these seams. Therefore,seamless molding is of advantage.

The expression that the shell materials are flexible, pliable andresilient is meant in a relative manner in comparison with the innerrigidifier component of the articles of manufacture, i.e. the fleshportions which are rela-.

tively rigid. The composite article itself is rigid and resistsindentation, chipping etc. The flesh portion rigidifies the flexibleshells and improves resistance to cold flow or heat distortion. Theshell materials protect the rigidifier flesh portion from fracture andimprove their resistance to impact. This mutual improving effect betweenshell and flesh materials is unexpected and surprising and the effectobtained could be described as synergistic.

From the shell materials discussed above, polyethylene andpolycarbonates, when blow molded, are used at a limited thickness. Inusing the various shell materials with the rigid foam inner rigidifiercomponent of this invention, the composite article manufactured showselimination of flexibility, improved resistance to impact and in manycases the tensile strength of the composite article shows improvementwhen compared separately with that of the shell or flesh material. Theseobservations apply to shells made of plastisols, flexible polyesters,flexible epoxy resins, polyethylene, polypropylene, polyallomers,polyurethane elastomers, rubber, polycarbonate, ethyl cellulose, methylmethacrylate, amongst others. The degree of the above discussedimprovements may vary according to the selection of the shell formingmaterial, its secondary compounding ingredients, thickness and shape ofthe shell, formulation of the flesh material and its thickness, amongstother factors.

According to a more recent type of molding method shells can be moldedby rotational casting of powders. Polyethylene in powder formillustrates suitability for this method. The powder is rotated to obtainuniform distribution over the interior surface of the mold. The mold isthen heated to obtain the required molding temperature.

For the purpose of forming the outer shell component the thermoplasticplastics materials are preferred. These are illustrated by plastisolsand polyethylene. For the purpose to form the inner rigidifier componentthe thermosetting rigid foams are preferred. The reactive vinylplastisol systems containing reactive acrylic monomers, discussedfurther above, are considered as thermoplastic for the purposes of thisinvention and are included in the preferred group of plastics for thepurpose of forming the outer shell component.

THE INNER RIGIDIFIER COMPONENT As described earlier, the flesh portionof the products of this invention is the inner rigidifier componentwhich in turn is snugly attached to the outer shell component and is inintimate contact therewith. The inner rigidifier component comprises arigid foam. One of the purposes of the application of the innerrigidifier component is to rigidify the outer shell component. Therigidifying action is of particular importance, where the outer shellcomponent is flexible, according to a favored embodiment of thisinvention. A further object of the inner rigidifier component is toreinforce the outer shell component and in many cases to provide bodyand structural stability to the composite article of manufacture.

Rigid plastics foams are well known in the art and are discussed e.g. byT. H. Ferrigno in Rigid Plastics Foams, Reinhold Publishing Corp., 1963.They are illustrated by rigid polyurethane foams, polystyrene foams,epoxy foams, polyvinyl chloride foams, phenolic resin foams, siliconefoams, syntactic foams, cellulose acetate foams, acrylic foams,polyester foams, asphalt foams, amongst others. These rigid plasticsfoams are not equally suitable for the instant invention. For thisreason they will be discussed individually. The favored foam systems areillustrated by the rigid polyurethane foams. They will be discussed atsome length.

et al., 1946, p. 310, 316 and 455 to 465. Some of the problemsencountered in this field of the art are discussed by 10 H. L. Heiss etal., Ind. Eng. Chem. 1954. Pages 1498 to 1503.

In the preparation of polyurethane foams several components are used.Some of the components permit the use of alternatives. One of thenecessary components is a compound containing free isocyanate (NCO)radicals. This component can be a polyisocyanate, usually adiisocyanate, or a reaction product thereof, containing free NCOradicals. Such reaction product is sometimes called an adduct or aprepolymer or a quasi-prepolymer, and is usually formed with a polyol.The second necessary component supplies active hydrogen atoms, suppliedby free hydroxyl groups derived from a polyol or from ahydroxyl-terminated polyester. The free hydroxyl groups are reactive.Alternatively polyesters or compounds containing reactive amine or COOHgroups can supply the active hydrogen contributing second component.When free hydroxyl groups or free carboxyl groups are reacted with freeisocyanate radicals, CO gas is formed in situ in the reaction which inturn acts as the foam forming gas. These types of foam are also known ascarbon dioxide blown foams. In many cases small quantities of Water arealso added to the reaction mixture in order to react with the free NCOgroups, forming again CO in situ. Ureas are frequently formed asintermediates, which react in turn with additional free NCO groups toyield urethanes or cause crosslinking of the polymers formed in thereaction. In many formulations catalysts are also present and optionallyauxiliary foamers or blowing agents may be added, liketrichlorofluoromethane.

Aryl diisocyanates are preferred, but alkyl diisocyanates may also beused. The most popular diisocyanates are the toluene diisocyanates, alsocalled tolylene diisocyanates. 2,4 tolylene diisocynaate and 2,6tolylene diisocyanate are frequently used in admixture with each otherand commercially available products include mixtures of these twoisomers in proportions of 60%-40%, 65%35%, 20%. The 2,4-tolylenediisocyanate is also produced in 99%l00% purity, and is also called TDI.The 80/20 and 65/35 mixtures are called TDI-Mixture, with the respectivepercentage identification added. Other diisocyanates are 3,3'-bitolylene4,4-diisocyanate (TODl);

diphenylmethane 4,4-diisocyanate (MDI);

( p,p'-diphenylmethane diisocyanate) polymethylene polyphenylisocyanate(PAPI, essentially a tri-functional polyisocyanate);

1-chlorophenyl-2,4-diisocyanate;

diphenyl-4,6,4'-triisocyanate;

l,6-hexamethylenediisocyanate;

p-dixylyl methane-4,4'-diisocyanate,

di- (p-isocyanylcyclohexyl) methane;

tri- (p-isocyanylphenyl) methane.

The principal commercially available polyhydroxy compounds are ethyleneoxide and propylene oxide adducts of polyfunctional active hydrogencompounds such as glycerine, sorbitol, trimethylolpropane, ethylenediamine, sucrose, etc. These compounds are polyethers, but since theyare primarily polyols, the term polyether polyol is properly used. Rigidfoams require the use of highly functional reactants. These are mostuseful when based upon polyalcohols having functionalities of at least 3and in many cases greater than 3. The fluidity of these reactants atambient temperatures is important as most of the time the reaction iscarried out at room temperature and in the absence of diluents. AtlasChemical Industries offers proplyene oxide condensates, triols, hexols,pentols and other polyols. Wyandotte Chemical Corp. markets a variety ofpolyether polyols, which are propylene oxide or ethylene oxidederivatives based on trimethylol-propane or on glycerol, or onpentaerythritol, or on sorbitol. In one type of polyether polyolsmarketed by Dow Chemical Co., sucrose is reacted with propylene oxide,yielding cyclic polyfunctional polyether polyols. Olin-MathiesonChemical Corp. offers 0,0'-bis(diethanolaminomethyl)-p-nonylphenol. 1,2,6-hexanetriol is another example of usable polyols.

Various hydroxyl, carboxyl and amide bearing compounds may be reactedwith polyisocyanates to form rigid foams. Pittsburgh Plate Glass Companymarkets Selectrofoam Resin 6002, which is a high viscosity saturatedpolyester resin, compatible with toluene diisocyanates. In spite of itshigh viscosity, it exhibits fair mixing properties in batch-typeprocesses. It has a Hydroxyl Number of 440. Products have been preparedprimarily for flame-proofing purposes which can replace part of thepolyether polyol in the reaction. They are propylene oxide condensationproducts of aryl or alkyl phosphonates, like di-polyoxypropylenephenylphosphonate and di-polyoxypropylene chloromethylphosphonate. Analkyd, containing free carboxyl groups and reactive with diisocyanates,was prepared in Germany according to De Bell, from 2 /2 mols of adipicacid, /z mol phthalic anhydride and 4 mols of trimethylolpropane, havingan acid number of 35 and containing residual water.

As the handling of diisocyanates requires special and skilled care andprecautionary measures it became useful to pre-react the diisocyanatesprior to foaming and to complete the reaction in a subsequent step. Whenpolyesters and less effective catalysts are used in the reaction, it isadvantageous to prepare prepolymers. In this case the polymerizationreaction is partially completed prior to foaming, and therefore lessheat of reaction is generated during the foaming step than in theone-shot method. This is advantageous in high density foam preparation,like 6 p.c.f. (pounds per cubic foot) or higher. In preparing theprepolymer a polyester of known hydroxyl number is charged into ajacketed, agitator-equipped, glass lined or stainless steel reactionkettle which has been flushed free of moisture by dry air or drynitrogen. The following is an illustration of proportions: (1) 91.7parts by wt. of TDI with combining weight of 87.4 excess), (2) 87.5parts by weight of polyester with a combined hydroxyl number and acidnumber of 450 and having a combining weight of 125, and (3) 2.7 weightparts of water, having a combining weight of 9. The reactants are mixedat room temperature, the exothermic reaction is permitted to decline andthe batch is held at about 100 C. for approximately one hour. -It isadvantageous to keep the water out from the initial reaction and toprevent entry of airborne moisture. The water is added prior to foamingin combination with the catalystemulsifier mixture. Excess freeisocyanate (NCO) content is usually about 5%, but depends on the amountof water to be used in the foaming reaction. The prepolymers overcomethe handling of noxious diisocyanate in the foam producing plants. Theyare, however, very viscous, present problems in pumping and requiresmall proportions of addition of catalyst-emulsifier mixture, such as aratio of 2 to 100 parts of prepolymer. This makes the meteringdifiicult.

The introduction of quasi-prepolymers or partial prepolymers representsan advantageous progress in rigid foam technology. They are preferredfor the instant invention. They are particularly advantageous withthermoplastic shell components. The quasi-prepolymers are usuallyprepared by reacting of about 4 to 4.5 equivalent weights ofdiisocyanate with 1 equivalent weight of polyether polyol. When usingTDI, it is customary to mix all of the diisocyanate with one-half of thepolyol earmarked for the reaction and to allow the exothermic reactionto subside and then add the remainder of the polyether polyol. The batchis then adjusted to a temperature of 70 C. and maintained at thattemperature for an hour. Moderate agitation is used during the reactionand dry inert atmosphere is provided. The viscosity of thequasiprepolymers ranges, in most cases, between about 4000 and about7500 cps., with a tolerance of 1000 cps.- for a given grade. If excessTDI is added, the addition may bring the viscosities down to 100 cps. orless. The quasiprepolymer is reacted with the proper quantity ofadditional polyether polyol just prior to the foaming operation. Theadvantages of using quasi-prepolymers are numerous. Some of these are asfollows: good storage stability of the ultimate reactants; reduction ofthe exo thermic reaction; reduction of the noxious property of TDI andthe ability to produce uniform foams with primitive mixing equipment.

Quasi-prepolymers may be formulated into delayed action one-part systemsby partial blocking of the prepolymer with tertiary-tbutyl alcohol.Boric acid, surfactant and catalyst are added. Such blocked compositionsare stable at room temperature and produce rigid foams when heated toelevated temperatures, such as C.

The rigid foam forming compositions may contain other ingredients inaddition to the diisocyanate component and the component reactivetherewith. Catalysts, surface-active agents and additional blowingagents are illustrative of such other additives.

The catalysts promote the reaction, shorten reaction time and channelthe reaction towards the proper and desired end product. Examples ofN-containing catalysts are N-methylmorpholine, N-ethylmorpholine,triethylenediamine, diethylethanolamine, dimethylethanolamine,triethylamine, and N,N,N,N'-tetramethyl 1,3 butanediamine. The aminesare active at pH ranges of 10 and higher. Metallic catalysts areillustrated by stannous chloride, stannous octoate, ferricacetylacetonate, tri-nbutyltin acetonate, bis(2-ethylhexyl)tin oxide,di-n-butyltin diacetate, di-n-butyltin dilaurate, dimethyltindichloride. Synergistic effects are obtained by using certain organo-tincompounds with tertiary amines. For instance the mixture of 1mol-percent trimethylamine combined with 0.001 mol-percent ofdi-n-butyltin diacetate have a greater relative activity than either onealone, used in the same mol-percent ratio. In general it may be stated,that rigid foams require lower concentrations of catalysts than doflexible foams.

When water is added to polyester prepolymers to provide carbon dioxideblowing, difficulties are encountered, as water is not readilydispersible in such systems. Various nonionic and anionic surface-activeagents are found effective to act as emulsifying and wetting agents.With polyether polyols the viscosities are lower, still surfaceactiveagents are useful to provide uniform foam cell structure in rigid foams.The preferred surface-active agents nowadays are organo-silicone fluids.They are organo-silicone block copolymers. Dimethyl-silicone oil is onedesignation. These silicone compounds are soluble in water,polyisocyanates, quasi-prepolymers, trichlorofluoromethane and amines,and are dispersible in polyether polyols and organo-tin catalysts. DowCorning 113 is a silicone-glycol copolymer, specifically developed forrigid polyurethane foams. General Electrics SF-1034 and XF1066 arecopolymers of dimethyl polysiloxane and polyalkylene ether. They havesurface-active properties. Silicone surfactants are usually used inproportions of 0.5% to 1% of the total weight of the foam ingredients.In some cases the proportion may be lowered to 0.25%. The siliconespromote bubble formation, equalize surface tension on the surface of thebubble, impart resilience to the film and promote resistance to collapsewhen distorted during the rising of the foam.

Halocarbons are used as additional blowing agents. The same types can beused as in refrigeration: CCl F, CCl F and CCl F-CClF For the purposesof this invention trichlorofluoromethane is most advantageous, as itsboiling point and evaporation characteristics are the most suitable forworking close to room temperature. Advantageously halocarbons have lowthermal conductivity and this increases with temperature rise to alesser degree than it does with CO or air. They have a high degree ofhydrolytic stability and do not dissolve water. By their lack ofhygroscopicity they reduce the susceptibility of prepolymers orquasi-prepolymers to air-borne moisture. Co -blown foams cannot beproduced reliably at low den- 13 sities. Their practical lower limit isabout 4 p.c.f. (lb./cu. ft.). For economic reasons the preferred formdensities in this invention are about 1- /2 to 3 p.c.f. These can beformed with good uniformity by using halocarbon blowing agents.

Flame retardants are another group of additives. Whereas phosphoniumcompounds with reactive OH groups are available to replace part of thepolyether polyol reactant component, the trade frequently usesplasticizer type additives which are non-reactive with NCO groups, toobtain flame retardant properties. Examples are:tris-(2,3-dibromopropyl)phosphate and tris-(chloroethyl)phosphate.

For various specific effects other additives may also be present, suchas cellulose derivatives to control bubble formation, and comminutedminerals to assist in reducing shrinkage after foam formation. Hydrousaluminum silicates and kaolinite illustrate the latter group.

Manufacturing methods and problems related to the instant invention willbe discussed further below. These will be illustrated by rigidpolyurethane foams. At this point it is logical to discuss othersuitable rigid plastic foams. Before doing so, a few facts have to bepointed out, to explain the difference in degree of. applicability ofthese rigid foams to the instant invention. The shell component of theherein claimed article of manufacture is molded of a pliable plastics.The pliable plastics are in many cases thermoplastic and may require amold not only in the step preparing the shell component but also in thefoaming step, should elevated temperatures be needed either for thefoaming step or for the after-curing of the rigid foam. The use of amold during the foaming step is required to prevent deformation of themolded skin, providing the shell is thermoplastic and the foaming steprequires elevated temperatures. The use of molds during the foaming steppresents several problems. As the foam solidifies, the mold has to be atleast a two-piece mold in order to permit removal of the article ofmanufacture. If undercuts are present in the article of manufacture, amulti-piece mold is required or the mold has to be disposable andremovable by e.g. fracturing. Such multi-piece molds are expensive. Themolds, if permanent, are tied up for long periods and prevent massproduction techniques. The foam-in-place method of foam production isthe most advantageous for this invention. From these considerations itfollows, that if foam production can be carried out in the absence ofmolds and the molded skins themselves can be used alone for thefoam-in-place method, great advantages are derived in producing thearticles of manufacture of this invention. It also follows that the typeof foam where higher temperatures are required and expensive molds areinvolved is less attractive for this invention.

(2) Polystyrene rigid foams Polystyrene is readily available. Its rigidfoams are less adaptable to the preferred mass production techniques ofthis invention than polyurethane foams. Polystyrene foams cannot beapplied with ease with the foam-in-place method. They require theapplication of heat. This places limitations on their use. Smaller batchmixing operations can not be carried out with them either.

The extrusion techniques is one method to prepare rigid polystyrenefoams. It injects a volatile liquid, like methyl chloride into thepolymer melt and the melt expands upon release of pressure and coolsrapidly. This method produces a low density product. It is moreadaptable to producing slabs which then can be placed mechanically intothe shells and attached thereto by the aid of adhesives.

In another method styrene is polymerized, containing the foaming agent,in an aqueous emulsion and beads or rounded granules are produced. Thebeads so formed are filtered and washed. Hydrocarbon blowing agents canbe used, such as pentane, hexane or heptane. The blowing agent shouldboil below or at the softening point of the polymer. This can beillustrated by the temperature of 175 F. Diethyl ether and ethanolmixture is also used, by first preparing the granules and then soakingthem in the solvent. Petroleum ether yields less than 1 p.c.f. foamsusing 6-8% of the blowing agent. Alkyl phenol polyoxyethylenecondensation products or oil soluble higher alcohols (C to C are usedfor specific purposes. This type is called expandable polystyrene.Pre-expansion or pre-foaming is advisable if low density foams are to beproduced. One of the molding methods is the steam chest method. For thepurposes of this invention one can expand polystyrene beads inside themolded shell and adjacent thereto. The shell component is placed in asuitable mold, the polystyrene beads are placed into the shell and heatis applied to accomplish the expansion. An adhesive layer may beadvantageously used in between the shell component and the foam tosecure proper shrinkage relationship between the two components.

Injection molding can be carried out with expandable polystyrenecontaining a halocarbon blowing agent. This is not too applicable to theinstant invention. Blow mold-.

ing, beginning with an extrusion operation is also a method. 0.2% citricacid monohydrate and 0.25% sodium bicarbonate is used as microcellgenerating additives.

When a prefabricated foamed object is bonded to molded shells, drying,setting or hot melt adhesives may be used to accomplish the bonding.

(3) Rigid epoxy foams The commercially available epoxy resins arecondensation products of epichlorhydrin and bisphenol A. They arepolymerized to different molecular weights and range from liquids tohard fragile solids. Epon 828 illustrates a commercial product useful inpreparation of rigid foams from liquid compositions. It has a viscosityof 50 to 1-50 poises at 25 C. and an epoxide equivalent of 175 to 210.Typical examples of highly reactive curing agents are diethylenetriamine and triethylene tetramine. For specific purposes other curingagents may be used, such as aromatic polyamines, ethoxylated andcyanoethylated amines, tertiary amines, cyclic amines, acid anhydridesand amine terminated polyamides, amongst others. Difunctional curingagents would be expected to yield linear polymers with the difunctionalepoxy resins. However, tertiary amines promote crosslinking betweenpolyfunctional amines and epoxy resins. The presence of hydroxyl groupsaccelerates the reaction. High density foams can be based on Epon 828and prepared by using nitrogen releasing organic compounds as blowingagents, an emulsifier, a solvent to reduce the exothermic reactiontemperatures and a polyamine curing agent. The resin has to be preheatedto about C. and this imposes limitation on its use. In low density foamshalocarbon blowing agents are used. Silicone surface active agentsassist in simplifying and extending the use of epoxy foams. Halocarbon11 (fluorotrichloromethane, also called trichlorofiuoromethane) yields 2p.c.f. foams with ease.

Foam-in-place systems are available from various suppliers. They aremarketed as proprietary products. They are supplied as resin and curingagent. The resin component must be kept at 65 F. prior to mixing toprevent loss of the halocarbon blowing agent. Initiation time for startof foam rising is 30 seconds and foaming is completed in 1 to 3 minutes.The foam can be handled in 15 minutes but keeping it in a mold for about2 hours is recommended. Foam spray compositions are also available. Theepoxy foams have excellent adhesion properties to various surfaces withwhich they are in contact while still liquid.

(4) Polyvinyl chloride resin rigid foams Polyvinyl chloride (PVC) resinsand copolymers are popular members of the plastics family. There aredifficulties in their processing to foams, although their properties aredesirable in rigid foams. There are two grades on the market of interestin rigid foam manufacturing. One of them is a vinyl dispersion resincontaining about of vinyl acetate as part of the copolymer with PVC.This resin is very rigid and plasticizers are used to obtain therequired properties. The other resin is called Type I, low molecularweight resin and is essentially a low molecular polyvinyl chloride. Thesolvated gas process requires pressures of up to 300 atmospheres andapplication of a pressure vessel. This is not suitable for the instantprocess when low production cost is an aim. The gas releasing agentprocess has better possibilities. Gas evolving blowing agents are used,such as nitrogen compounds. The decomposition temperature is about 100C. Compounding on a cold 2-roll rubber mill of the following compositionyields a useful product: 100 weight parts of PVC dispersion grade resin(GEON 121), 70 weight parts of acetone, weight parts of dibasic leadphosphite stabilizer, 25 weight parts of NITROSAN, which is a 70/30mixture of N,N-din1ethyl-, N,N-dinitrosoterephthalamide/white mineraloil. The density of 2 to 2 /2 p.c.f. can be achieved with thiscomposition. The ingredients, less the acetone, are blended and theacetone is then added. The mixture is homogenized by one pass throughthe 2-roll mill. Metal molds heated 10 minutes with 100 p.s.i. steam areused and the molds are cooled. Heating the mixture for -20 minutes at100 C. completes the foam expansion. The shell forming materials have tobe properly selected to withstand these conditions, providingfoam-in-place process is used. Other solvents can replace the acetone.Other blowing agents are also operative, like azobisisobutyronitrile,azoamides, nitroso compounds, etc. Crosslinked plasticizer modified PVCfoams are produced by the aid of epoxidized oil (soya) as theplasticizer, which crosslinks upon heating. In this system pyromelliticdianhydride is recommended as the curing agent. This type of foamrequires curing temperatures up to 163 C. (374 R), which excludes itfrom many of the uses herein contemplated.

(5) Phenolic resin rigid foams Phenolic foams are made from casting typephenolic resins containing between 1.2 and 3.0 mols of formaldehyde permol of phenol. For foaming agents carbonate salts are used, such assodium, potassium, ammonium, calcium, magnesium and other carbonates.The intermediate casting resins are commonly called resoles. Many of thecarbonates have to be added just prior to foaming. Others may beincorporated into the resin, providing it is neutralized to a pH of 7 orhigher. Acid catalyst is then used, which promotes the evolution ofcarbon dioxide. Metal powders may be used to generate hydrogen gas asthe blowing agent. This presents the need for safety precautions.Organic gas generating agents are controlled with greater ease. Examplesare: p,p-oxybis(benzenesulfonylhydrazide), dinitrosopentamethylenetetramine and diazonium salts, such as benzene diazoniumsulfate. Air has also been utilized as well as other agents, likehydrogen sulfide, halogenated hydrocarbons, etc. The acid curing resinfoam is dried and cured after being foamed by the gas. Surface activeagents are added to secure uniform cell structure. Alkyl aryl sulfatesand sulfonates, alkylene oxide-phenol condensation products and lecithinare examples. The phenolic foams are usually brittle at low foamdensities. With many types post curing is required, e.g. for 8 to 10hours at 140 to 200 F. They can be foamed-in-place. They are lessadaptable for the purposes of this invention than the rigid polyurethanefoams, but with proper care of formulation and processing method, theycan be used.

(6) Urea-formaldehyde rigid foams Various methods have been used toproduce ureaformaldehyde resin foams. The liquid resin is filled withair or gas under agitation, while in water solution, with surfactantsand acid catalysts present. Gas can also be dissolved under pressure inthe liquid resin. In one recent development low boiling liquids areemulsified in the liquid resin. The resin contains dibutyl phenyl-phenolsodium disulfonate as the emulsifier. Halocarbons or propane areemulsified into the solution under pressure at low temperatures. Uponaddition of a catalyst, like phosphoric acid, the exothermic reactionvolatilizes the emulsified liquid and causes foam formation. This typeof foam is closed celled, whereas other foaming systems cause formationof open cells. The liquid blowing agents are used in proportions of 2 to30% based upon the weight of the resin solids. Polyethylene glycols areadded to increase the toughness of these otherwise brittle foams. Whenproperly plasticized, these foams make useful products for the purposesof this invention. Low temperature curing resin formulations arepreferred.

(7) Rigid silicone foams The polymers forming the silicone foams aresilicone oxygen compounds, like siloxanes. They are in the moreexpensive range and are used where good electrical insulatingproperties, low water absorption, good thermal stability are required.The polyorganosiloxanes can be powders or liquid. Foaming-in-placerequires surface treatment of the cavity of the skins to secureadhesion. The foams can be coated with silicone elastomers for maximumtemperature resistance. High temperatures are required to produce andset these foams, all equal to or above 300 F. and this reduces theirusefulness in many of the applications herein contemplated. As hydrogenevolves in many cases, precautions for safety of the operation arerequired.

(8) Polyester rigid foams It is difficult to foam polyesters by currenttechniques. The start of polymerization causes a stiff gel to form,which is not readily expanded by foaming agents. The polyesters arethermosetting partial polymers having high molecular weights comparedwith urethane prepolymers and epoxy resins. Even if the degree ofpolymerization is as low as 5%, the gel is non-thermoplastic and rigidand will not deform as the blowing agent vaporizes of releases gas.Polyesters containing residual hydroxy and carboxyl end groups reactwith diisocyanates and such hybrid polymers can be foamed by carbondioxide evolution or by the incorporation of halocarbons. Surfactants,water and peroxides are present frequently in such foaming operations.Ways and means are being developed to foam polyesters. One method e.g.,is using methacrylic acid polyesters exposed to ionizing radiation.Decomposition and polymerization set in simultaneously causing thepolyester to foam.

(9) Miscellaneous rigid foams Cellulose acetate foams were used inaircraft manufacture. The extrusion process is used utilizing a mixedliquid non-solvent (mixture of acetone and ethyl alcohol) at roomtemperature as the blowing agent and comminuted mineral of to 325 meshparticle size as the nucleating agent. The solvent mixture dissolvescellulose acetate at a temperature exceeding F. During the hot extrusionthe solvent plasticizes and simultaneously foams the resin. Whereas withthis method boards and rods can easily be manufactured, it is quitedifficult to adapt cellulose acetate foams for the purposes of thisinvention.

Rigid acrylic foams are suitable for coarse celled applications, wheremaximum resistance to degradation by ultraviolet radiation is required.Alpha-chloroacrylic acid ester polymers may be polymerized at roomtemperature. The polymer decomposes upon heating to 150 to C., to yieldan alkyl-chloride foaming agent. The internally generated foaming agentproduces foams of about 3 p.c.f. The inclusion of dimethyl siloxanepolymer surfactant for cell size control and addition of alcohol 17 orparaffin oil to the monomer prior to polymerization provides finer celldiameters.

Asphalt foams can be prepared by releasing gases under pressure intothis thermoplastic material in a manner similar to other foamedthermoplastics. In another method sodium bicarbonate is used as theblowing agent and aluminum stearate as a surfactant. By controlling theasphalt temperature carefully the gas release is obtained at a uniformrate and the gas is effectively entrapped. Special apparatus isavailable to heat the high melting asphalt and to inject gas or ablowing agent. The use of cold flow retarding agents is advantageous,like fillers, asbestos, gelation agents and high melting resins.

'Ebonite, which is hard rubber containing 30 to 40% sulfur can beexpanded by foaming. Plastics, having high softening points require highpressure equipment to contain the blowing agent and the polymer mixtureexpands upon sudden release of pressure. Polypropylene, polyamides andpolycarbonates can be foamed with variations of this method.

A special class of rigid foam is called syntactic foams. These dependfor foam formation on hollow microspheres or microballoons, and not onthe resin used for bonding. Two types of microballoons are available.One is based upon a phenolic resin and the other one upon silica. Thephenolic spheres have an average particle size diameter of 0.0017 inchand a particle size diameter range of 0.0002 to 0.005 inch. Bulk densityis 3 to 5 p.c.f., true sphere density of 12 p.c.f. The spheres arefilled with inert gas, such as nitrogen. Glass microballoons are beingmade under a license of Standard Oil Co. (Ohio). Microballoons areeasily incorporated into liquid thermosetting plastics, like epoxies orpolyesters. They form trowellable mixes and can be placed by hand toform sandwich structures. Room temperature curing polyesters andelastomers illustrate suitable binders. Densities of syntactic foams arenot as low as with foamed-in-place systems, as high density resin fillsthe interstices. 20 to 25 p.c.f. are illustrative densities. In theinstant process they could be used where the rigidifier foam is appliedas a comparatively thin layer and does not fill the cavity of the moldedshell fully. This limitation is primarily imposed by consideration ofeconomy.

SELECTION OF THE INNER RIGIDIFIER COMPONENT In selecting the rigidplastics foams, one has to consider the problems relating to thepreparation of the articles of manufacture of this invention. The outershell component is formed in a mold. During the foam producing operationin some cases the shell may be left in the original mold in which it wasprepared. In other cases the shell is removed from the mold prior to thefoam producing operation and the foam formation is carried out either ina second mold or without the aid of any mold, using the shell itselfalone in shaping the inner rigidifier foam component. The setting of therigid foam rigidifies the composite article of manufacture, and in orderto remove it from the mold after the foam has solidified, providing amold is used during this step, a multi-piece mold is required. Suchmolds are diflicult to operate and require precision tooling. Thereforeit is of great advantage if the inner rigidifier rigid plastics foamcomponent can be prepared in the absence of any mold, using the shellcomponent alone to shape it during its formation.

A further problem arises when the preparation of the foam or itsapplication requires temperatures at which the shell component maydeform. Additional problems relate to the shrinkage of the rigid foaminner rigidifier after the foaming has been completed. It is ofadvantage if the outer surface of the inner rigidifier foam compo nentremains in steady contact with the inner surface of the outer shellcomponent during and after preparation 18 of the end product. Thisrequires controlled shrinkage properties.

Foams having no predetermined confinement are known as free rise foams.The volume expansion of free rise foams is limited only by thethermodynamics and reaction rate of the system. In producing foams inthe interior of shells, as they are produced in the instant invention,the foam is always confined at least by the interior surface of theshell. In the instances where the cavity of the shell is fully filled bythe foam, the foam is fully confined with the exception of the accessopening (filling hole). In other instances an interior core or formassists in the confinement. In still other cases the foam is confined bythe interior of the shell on at least one surface and freely rises tofill the interior cavity. Any excess may force itself out of the accessopening. In the cases of foam confinement, distention and distortion ofpliable shells can result and, as a consequence, a reinforcing mold overthe shell may be required during the foaming operation. Free rise on theinterior surface does not extend a distending pressure on the shell.Thus, a reinforcing mold over the pliable shell is not necessary duringthe foaming operation. It can be seen that the absence of need for asecond mold during the foaming operation is of great advantage. In caseswhere the foam is otherwise totally confined, it can be noted that afterplacement of the foaming composition the filling hole can be blocked tobring about a mild back-pressure that can assist in forcing theexpanding foam to fill the interior spaces and undercuts.

To avoid excessive shrinkage of the inner rigidifier component during orafter its preparation is of importance for the success of the productsprepared hereunder. Quasiprepolymer and prepolymer rigid polyurethanefoam compositions are preferred, as they can be formulated with greaterease to produce low shrinkage. However, more recently, one-shot typerigid polyurethane formulations have also been formulated with lowshrinkage properties. It has been found, that efiicient but slow mixingof the foaming components reduces shrinkage. This can be achieved by theso called folding action mixing, using an up and down and front to backmotion, used for paint mixing. Machines are available to perform suchmixing with efficiency and within the required short periods before foamrise starts.

Based on some of the above considerations, rigid polyurethane foams areeminently suitable for the purposes of this invention. They permit aroom temperature initiated reaction. Means are available to reduce theheat of the exothermic reaction. The quasi-prepolymer systems permituniformity of foam structure and require only primitive mixingequipment. Compositions suitable for foam-in-place type application arealso available today from epoxy resin rigid foams. They are alsosuitable for spray application if properly compounded. Preheating of thecompositions to to C. is required.

Polyvinyl chloride type rigid foams can be prepared by various methods.The gas releasing agent process can be carried out at temperaturesaround 100 C. and molds can be heated by steam of 100 p.s.i. pressure.Foamin-place method is applicable and even rotational casting or slushcasting is possible. Gelling and fusing the rigid foam requirestemperatures which in turn require molds to prevent the deformation ofthe skin portion. Phenolic resin rigid foams can be prepared at roomtemperature and foam-in-place method is applicable. After-cure at l40200F. is advantageous and sometimes required. They are brittle by natureand may require plasticization. The urea-formaldehyde resin rigid foamscan be prepared at room temperature and are also brittle, but can beplasticized. Polystyrene can be used from expandable beads. However,heat is required in the nature of to 200 F. The beads are preheated to atemperature above the softening point of the polymer. Pre-expansion isadvantageous and heat is applied for completing the foaming and fusingthe outside walls of the beads together. Polystyrene is difiicult toapply by the foam-in-place method. Silicone foams require 300 F.temperatures or more. Low density polyethylene can form foams of lowdensities, such as 2 p.c.f., illustrated by Ethafoam of Dow Chemical. Itrequires elevated temperatures in manufacturing and it is hard to use bythe foam-in-place method. More recently room-temperature curing siliconefoams have been formulated of two liquid components. They are blendedand poured in place. The reaction is slightly exothermic buttemperatures rarely exceed 150 F. It requires hours or more forcompletion of the process. The list herein discussed is not a completeevaluation of all plastics rigid foams and their comparative values anddisadvantages, but merely an illustration of how to evaluate forsuitability.

The most preferred rigid plastics foam formers for the purposes of thisinvention are the rigid polyurethane foam compositions. The nextpreferred foam formers are the rigid epoxy resin foam compositions.Thermosetting foams are preferred over thermoplastic foams. Low curingtemperatures and fast foam setting rates are of advantage. The settingrate should not be so fast as to prevent adequate distribution of thefoaming composition throughout the inner surface of the outer shellcomponent. 1

PREPARATION AND APPLICATION OF RIGID PLASTIC FOAMS The preparation andapplication of rigid foams according to this invention will beillustrated with rigid polyurethane foams.

In one of the methods batch type equipment is used. Simple pails andsticks or propeller type agitators are used frequently to mix therequired ingredients where low volume pours are required. In such casesquasiprepolymer formulations are preferred as they permit proper controlof the rise time. In this method formulations are used which delay thereaction to start not earlier than one half minute after the ingredientsare mixed. The temperature of the prepolymer is usually between 70 and100 F. The polyether polyol component is usually maintained at about 65to 68 F. to prevent loss of the halocarbon blowing agent whose boilingpoint is around 75 F. The loss of blowing agent would result in higherdensity foams. The preferred p.c.f. does not exceed 3. In some casesfoams with p.c.f.s of up to 25 are useful. The ingredients are weightedout or proportioned by volume in separate clean containers. The cooledpolyether polyol is added to the prepolymer. Mixing is completed inabout seconds. Mixing with turbine or disc type mixing blades at about1000 r.p.m. for 15 to 25 seconds is illustrative. The mix is immediatelypoured after mixing and prior to the start of the foaming. The type ofcompounds supplied for batch mixing of two component systems rise tofull height in 3 to 5 minutes. Most formulations are designed to providea free rise of about 12 inches. Higher halocarbon concentrations areused for preparing thick sections.

Quasi-prepolymer two-package systems are marketed by various supplierswith varying qualities. As illustration the Nopcofoam H-l02N andNopcofoam H-103N systems are mentioned, supplied by Nopco ChemicalCompany. The components are marked as T-component and R-component. TheT-component is the quasi-prepolymer formed by the diisocyanate and apolyether polyol. It has reactive NCO groups and supplies the isocyanateradicals for the foaming reaction. The T-component may also containsurface active agents, such as the silicones. The R-component containsthe polyether polyols supplying additional OH-grouping for the foamingand polyurethane forming reaction. In this H-series the R-componentcontains the fluorocarbon blowing agent, the catalyst, such as N-ethylmorpholine and dibutyltin dilaurate and may also contain all or part ofthe surface active agents, such as the silicones. The suitablefluorocarbon is illustrated by Freon #11, which istrichlorofluoromethane, having a boiling point of about 74.7 F. TheH-series of Nopcofoam compounds have a fast curing cycle. Withformulation changes the curing speed and the p.c.f. of the resultingfoam may be varied. The same applies to start of the rise and rise timeof the foaming. Nopcofoam H103N supplies a rigid foam of about 3 p.c.f.and H102N supplies a rigid foam of about 2 p.c.f.

The foaming instructions are as follows for Nopcofoam H102N: Thetemperature of both components should not be higher than about 7075 F.The mixing ratio is about 52% R and 48% T, by weight. The R component ispoured into the T component in the proper weight ratio. This is followedby mixing with a high speed drill motor, having a minimum RPM of 1800,using proper mixing blades, such as an impeller type. Mixture becomescreamy white and volume increase is noticed in about 25 to 30 seconds.The shell, acting as a mold, may advantageously be preheated to to F.This is advantageous particularly where the foam has to fill areas ofsmall crosssection. The higher the temperature the more rapid thefoaming action. The foam cures at room temperature in about 24 hours.

The foaming instructions for Nopcofoam H-103N are similar to those ofH102N with regard to temperature, mixing, mixing time, and curing.However, the mixing proportions of the components are about 50%R-component and about 50% T-component, by weight. The average coredensity is 2.6 p.c.f.; the K Factor, Aged (B.t.u./hr./sq.ft./ F./in.thick) is 0.120; maximum recommended service temperature is 180 F.

Preparation of carbon dioxide blown rigid foams is illus trated by firstpreparing a prepolymer in two steps. In the first step the followingmaterials are added in the order shown to a clean and dry 12-1ite1'flask: 240 weight parts of tolylene diisocyanate (80/20 mixture of2,4/2,6 isomers) and 100 weight parts of Pluracol TP 440 Triol, urethanegrade with hydroxyl number of 400. The Pluracols are polyoxypropylenederivatives of trimethylolpropane, supplied by Wyandotte ChemicalsCorporation. They are available with varying molecular Weights and theyare characterized by their hydroxyl number. The one used herein has aviscosity of 625 cps. at 25 C. and an approximate molecular weight of418. As the above materials are mixed, the temperature rises due to anexothermic reaction. After the temperature rise subsides, thetemperature is adjusted to 100 C. and the mixture is held for 1 hour. Inthe second step the mixture is cooled to 60 C. and transferred to aclean and dry container for storage. The NCO/ OH ratio of the product is3.85/ 1.0. After aging for 24 hours the viscosity of this prepolymer at25 C. is 4000 cps.:1000 cps. and it has a free NCO content of 25% :O.4%.For the Foam Preparation the following ingredients are first premixed:

For product I II Component A:

Above prepolymer (25% free -NCO) l Silicone oil L-520 0 Component B:

Diethylethanolamine Water Pluracol TP 440 Quadrol polyol selves. Thequantity recommended for mixing at one time is 300 to 400 grams,depending on the foam density. The foam is allowed to rise and becomestack-free within 10 minutes. This type of foam is recomemnded to becured for about 2 hours at 70 C. By proper selection of faster catalyststhe curing temperature can be reduced even to room temperature. The coredensity for Product I is 1.8 p.c.f. and for Product II it is 2.8 p.c.f.The compressive strength at yield point in p.s.i. is 27.6 for Product Iand 49.0 for Product II.

The use of prepolymers can be illustrated by sprayable n'gid urethanefoam systems. The foaming system consists of two fluid intermediateswhich are mixed immediately before application to the target surface.The intermediates are (a) a liquid prepolymer, prepared by reacting apolyol with an organic diisocyanate and (b) a liquid catalyst whichcontains (1) a volatile blowing agent and (2) a curing agent for thefoam. Component (a) is placed in a pressure tank. A heat exchanger inthe delivery line warms the prepolymer to 130 F. Component (b) isthoroughly mixed and placed in a second pressure tank. A heat exchangermay also be used in this line to regulate its discharge temperature. Ina specially constructed spray gun, components are mixed externally inthe spray pattern after the materials leave the gun, but before theyreach the surface to be foam coated. The material begins foaming almostimmediately on the target surface, and rises to full foam height inabout 1 minute. The foam may be initially friable, but after curing,e.g. at 130 F. the friability disappears in 10-15 minutes. Pluracol TP440 and Quadrol permit the formulation of this type of composition. Foamdensities of from about 2 /2 to about 3 p.c.f. are practical. Properformulation provides for elimination of sagging on vertical surfaces.The elevated temperature of the prepolymer also promotes prevention ofsagging.

In the case of large scale production and where equipment cost permitsit, one-shot application is of advantage. Polymethylenepolyphenylisocyanate, supplied under the trademark of PAPI by the UpjohnCompany, Polymer Chemicals Division, is suitable to illustratesuccessful oneshot application for the pour-in-place or foam-in-placemethod of foam preparation. PAPI yields low exotherm one-shot systemspractical for conventional pour molding or spraying. It gives good earlystrength that allows quick handling of the end products. It has superiordimensional stability. Polyols suitable for use with PAPI includemethylglucoside, sorbitol, sucrose, amine-derived cross-linking agents,phosphorus-derived resins and polyesters. Suitable catalysts includetetramethylguanidine, trimethyl piperazine, dimethylethanolamine,triethylamine, dibutyltin dilaurate, stannous octoate, dibutyltindiacetate, amongst others. Suitable silicone co-polymers are Dow CorningCorporations DC-201, Union Carbides L-520 and L 530 and GeneralElectrics XF-1066. As blowing agents fluorocarbon 11 (F41) and inhibitedF-l 1, i.e. F-11B are suitable for illustrative purposes. Otherfluorocarbons may also be used. Table 1 shows a few illustrativeexamples of PAPI based one-shot rigid urethane foams. Parts are byweight.

Dimethylethanolamine.

Fluorocarbon 11B PAPI (NOO/OH=1.05/1) Processing:

Resin component temp, F..-

PAPI component temp, F 110 115 Molding temperature, I 110 115 Overalldensity, p.e.f 2. 45 2.

22 Formulation for non-self-extinguishing foam suitable for sprayapplication is given in Table 2.

TABLE 2 Weight parts PAPI 110.00 Polyfunctional polyglycol Hydroxyl No.450 100.00 Silicone DC-20l 2.00 Fluorocarbon 11B 40.00Tetramethylguanidine 2.00 DABCO (triethylenediamine) 1.50 Dibutyltindiacetate 0.30

Processing data NCO ratio 1.05. Resin stream temperature F. PAPI streamtemperature 75 F. Throughput lbs/minute 5.50. Cream timeseconds 3 to 4.Rise time-seconds 7. Tack free timeseconds 7. Core density-psi 2. Closedcells As has been demonstrated, rigid polyurethane foam layers can beprepared according to this invention by any one of the major knownmethods: (1) quasi-prepolymer method, (2) prepolymer method and (3) theoneshot method. The quasi-prepolymer method is preferred. Theapplication by poured-in-place or foamed-in-place method issatisfactory. Spray application is usable. Slush casting or rotationalcasting may be used in many instances.

The products of this invention require special care in many respects.Foaming and curing at temperatures where the molded skins do not deformhave an advantage and permit the elimination of the use of an outsidemold during foaming. It increases ease and economy of production itfoam-in-place filling of shells can be accomplished while the fillinghole of the mold remains open to the atmosphere. Conversely, the closingof molds and introducing pressures above 15 lbs. square inch becomesmore difiicult and less attractive.

With regard to shrinkage, no problem arises after curing if the innerlayer foam shrinks at the same rate as the shell. If the foam shrinks ina different degree and particularly if it shrinks more than the shellafter the molding operation is completed, an unacceptable product may beobtained. Therefore, preventive methods of manufacture are warranted toblock excessive shrinkage of the foam and formulation is adapted toavoid excessive shrinkage. During the period that the foam risespressure is exercised by the foam. To prevent deformation of the moldedskin caused by such excessive pressure is also important. In some casesthe shells are backed up by a mold during the foaming operation toprevent such deformation. Proper formulation of the foaming compositionscan contribute greatly to the solution of these problems. However, inmany instances manufacturing steps or mechan ical means are used toovercome possible difiiculties. Some of these are discussed below inconnection with the drawmgs.

Whereas in most cases the rigid foam snugly attaches itself to themolded shell, in some cases it is of advantage to apply an adhesivelayer between the shell and foam to overcome possible effects ofexcessive shrinkage. A great variety of adhesives may be used. Hotasphalt or other hot adhesives are illustrative. Suitable adhesive typesare further illustrated by resorcinol adhesives, rubber emulsions,rubber solutions, epoxy resins, polyester resins, latex, latex modifiedcements, amongst others. The adhesive causes the shell either to shrinkwith the foam or, providing the shell is strong enough, the adhesivecauses the foam to adhere to the surface of the shell and prevents theformer from shrinking away from the surface.

A special type of foaming is known in the art as frothing. It is appliedby mixing machines, using Freon 12 (CCl F as blowing agent. Because ofthe low boiling point of this blowing agent, it is applied by a thirdline leading from a cooled pressure tank to the mixing head of themachine. A part of the foaming occurs in the mixing head and the rest inthe piece or mold. The percentual distribution between foaming in thehead and in the piece can be regulated by formulation. A 50:50percentual proportion is illustrative. Frothing falls under the terms ofpour-in-place and in situ foaming. It is characterized by lower foamrise and development of a lesser pressure during the foaming-in-placeoperation. As a consequence, it causes less distortion of the shellcomponent. Frothing is harder to control than other conventionalfoaming. It may simultaneously develop small and large cells, therebycausing some uneven material. The method is more adaptable to formlarger objects with large foam volumes. The difliculty of starting andstopping this type of operation, with equipment available at thepresent, more or less excludes it from the useful range of making smallobjects. Frothing can yield lower rigid foam densities than attainableby other methods.

After reviewing some of the considerations further above it is apparentthat the absence of need for a second mold during foaming is of greatadvantage. Some of the advantages may be summarized as follows: (1) Easeof production of the composite articles of manufacture; (2) possibilityof producing composite articles of manufacture with complicatedundercuts which could not be removed from a one-piece or multi-piecesecond mold with the required ease; and (3) savings of the requiredlabor and mold cost. According to this invention many factors may assistto eliminate the need for a reinforcing mold during the foaming step.One factor is the proper and correct formulation of the foamingcomposition to achieve radical lowering of the foaming pressure. Thepressures of foams in rising can vary considerably. If excessivepressure develops, distention and distortion of the premolded shellcomponent may occur. Proper formulation achieves minimal shrinkage,minimal pressure development during foaming and low polymerizationtemperatures. With such a composition the foaming-in-place operation canbe carried out with ease without the application of a reinforcing moldduring the foaming operation. Another factor is to increase theresistance of the shells to distorting pressure by, for example,increasing the wall thickness of the shells or utilizing more rigidtypes of plastisol, such as those containing reactive acrylic monomers.The latter type yields shells which are still thermoplastic and pliable,but their deformation temperature is raised to a range of from about 138F. to about 150 F. As they are considerably more rigid at roomtemperature than other more conventional plastisols, they have a greaterresistance to foam pressures without showing distortion. Still anotherfactor is the size of the access opening. In many instances where theshape and planned use of the composite article of manufacture permitsthe increase of the relative size of the access opening, such increasereduces the foaming pressure and permits the elimination of the secondor reinforcing mold during the foaming step.

Generally speaking requirement for a second reinforcing mold during thefoam-in-place operation exists where the composite article ofmanufacture is large in size (like when it exceeds in one dimension 1 or2 feet), or has numerous flat surfaces. Even in cases of large shellsand shells that are particularly pliable, due to formulation orcomparatively thin wall thickness, I have found it possible to avoid theneed for a second mold by slush casting or rotational casting ofincremental layers of rigid polyurethane foam against the interior shellsurface. By applying several layers of comparatively thin coats of foamin succession a thick enough rigidifier component can be produced tomeet the requirements. No excessive pressure builds up and as aconsequence distortion is avoided. A

similar effect can be obtained by placing a core in the interior of theshell cavity and foaming-in-place between the core and the interiorsurface of the shell. The core may be of a plastics skin orpaper-chipboard, amongst others. The pressures exerted are lowered inthis case by the reduced volume and thickness of the foam wall betweenthe shell and the core. In a related embodiment incremental horizontalsuccessive filling of foam layers is applied and as a result thedistorting or distending pressure of the foam on the shell is reduced toa degree eliminating the need for a reinforcing mold during foamapplication.

ANCILLARY REINFORCING ELEMENT (SPINE) When the outer shell component andthe inner rigidifier component jointly form a cavity the presence of anancillary reinforcing element may be useful and desirable. Its utilityoccurs when the composite article of manufacture is exposed to strongstresses and pressures. Such an ancillary reinforcing element assiststhe rigidifying action of the inner component and toughens the compositearticle of manufacture. In my prior applications this element was calledreinforcing spine. This ancillary reinforcing element may be of metal,paper-chipboard, cardboard or a synthetic resin layer, amongst othersuitable materials. The element may be continuous or discontinuous. Whenit is continuous, it may be applied by casting, such as slush casting orrotational casting. Low melting point metal alloys, used as ancillaryreinforcing elements, may be applied by casting. The same applies to thesuitable synthetic resin compositions, illustrated by polyester resinsand essentially flexible epoxy resins. In many instances, metals with amelting point of around 700 F. may be successfully cast into cavitiesformed jointly by outer and inner components. This can be explained bythe cooling action of the system forming the joint cavity on the castthin metal layer required.

The epoxy resins and polyester resins coat the entire interior surfaceof the joint cavity and are advantageously applied by casting. Theyimprove to a great extent the resistance of the composite articles ofmanufacture to the following stresses: impact, flexing, compression andtension. A few illustrative examples of suitable compositions to formsuch ancillary reinforcing elements (AR-E) from synthetic resins aregiven below (percentages are by weight).

Example ARE-No. 1: 12.4% of Laminac Polyester Resin #4128, 37.2% ofLaminac Polyester Resin EPX- 126-3, 0.1% Cobalt Naphthenate with 6%metal content, 49.3% Flint (silica) 325 mesh grade and 1% of MEKperoxide, totaling This composition can be slush cast at roomtemperature and it sets in about 10 to 15 minutes. By reducing thequantity of cobalt and MEK peroxide the setting time can be extended.

Example ARENo. 2: Example A-R-E-NO. l is repeated with the change thatthe resin component is entirely 49.6% of Laminac Polyester ResinEPX-126-3, the other ingredients remaining unchanged. This compositionproduces a more flexible resin layer than the preceding example and ispreferred. Some of the ingredients are described in greater detail underthe Shell Components under Example D.

Flexible epoxy resin compositions for the use of ancillary reinforcingelements are preferred to the polyester compositions. The epoxycompositions can be applied by slush casting and they set overnight atroom temperature to a suflicient degree so that the articles can behandled. Complete polymerization is achieved in an additional few days.The epoxy layers are very tough.

Example A-RE-No. 3: A flexible epoxy resin composition is made of thefollowing ingredients: 15.05% EPON Resin 871, 15.05% EPON Resin 828,6.15% Epoxide #7 (an epoxy plasticizer of Procter & Gamble), 30.2% of325 mesh grade Silica, 30.2% of 60 mesh grade Silica, 3.0%Diniethylenetriamine (DTA) and 0.35%

Cab-O-Sil, totaling 100%. Some of the ingredients are described ingreater detail in Example C of the shell component. The Cab-O-Silregulates viscosity, flow and stoppage of flow.

An illustration of desirable thickness for the resinous ancillaryreinforcing elements is from about 15 /2 mils to about 250 mils. Many ofthe resinous compositions can be applied by spraying.

In the drawings:

FIG. 1 is a vertical cross-sectional view of a single piece moldutilized in the present invention to prepare the shell portion. 13 isthe metal mold and it shows an undercut.

FIG. 2 is a vertical cross-sectional view of the mold of FIG. 1. Shell14 is molded in mold 13.

FIG. 3 is a vertical cross-sectional view of the mold 13 of FIG. 1,illustrating the removal of the plastisol shell 14 from the mold. Theshell is in a somewhat collapsed and distorted state at the removaltemperature, but regains its original molded shape after removal andcooling to room temperature.

FIG. 4 shows the plastisol shell 14 after removal from the metal mold 13according to FIG. 3. Rigid foam 15 fills out the cavity of the moldedshell 14. The shell is protected during the foaming operation by aplaster of paris mold 16 which has been applied to the molded shelle.g., by dipping, prior to foaming. For this purpose the shell is dippedin a liquid plaster mixture, providing contact between the outsidesurface of the shell and the plaster mixture. The plaster mixture isallowed to solidify. The foaming composition is then placed into thecavity of the shell and allowed to foam-in-place.

FIG. 5 shows the vertical cross-sectional view of the composite articleof manufacture of FIG. 4, with the shell 14 and the rigid foam 15, afterthe plaster of paris mold of FIG. 4 has been removed by cracking andpeeling.

It may be noted, that in FIG. 4 low temperature melting metal alloys,such as manufactured by the Cerro Corporation, can be sprayed on theshells, to replace the plaster of paris layer. After the rigid foamcomposition solidifies and cures in the cavity of the shell the metalcan be melted off at low temperatures and recovered. This alternativerequires proper correlation between the melting point of the lowtemperature melting metal alloy and the maximum temperature to which theshell material can be exposed without permanent damage.

FIG. 6 is identical with FIG. 5 of the copending parent application Ser.No. 22,002 referred to above and illustrates the verticalcross-sectional view of an article manufactured according to thisinvention. 14 is the molded plastisol shell. 15 is a rigid polyurethanefoam inner rigidifier component which fills out the cavity of the moldedplastisol shell. 17 illustrates weights which are suspended in the rigidpolyurethane foam. They serve to reduce the quantity of the requiredpolyurethane foam, reduce shrinkage and may also increase the weight ofthe composite article of manufacture. The inexpensive scrap weights areselected from products having suitable density and may be illustrated bywood scrap, such as wood ends from boards cut into cubes, or cardboardobjects of various shapes. These scrap pieces are placed into the cavityof the molded shell prior to solidification of the rigid foam eitherprior to pouring of the foam composition or shortly thereafter. They mayalso be premixed with the foam composition or one of its components. Auniform distribution of these weights in the foam composition isdesirable. This goal can be achieved with ease.

FIG. 7 illustrates a vertical cross-sectional view of a compositearticle of manufacture of this invention at the manufacturing stage. 18illustrates a two-piece mold in which the plastisol shell 14 is molded.15 is the rigid polyurethane foam. The shell is kept in place in themold while the composition forming the rigid polyurethane foam ispoured-in-place and foamed-in-place in the molded shell. The compositearticle of manufacture is removed from the mold only after themanufacturing is fully completed and the foam is cured. For removal, thetwo-piece mold is taken apart. To facilitate removal, the mold surfacemay contain a mold release lubricant, or air pressure may be appliedbetween mold surface and shell.

FIG. 8 illustrates a vertical cross-sectional view of a compositearticle of manufacture of this invention. 14 is the molded outer shellcomponent. 19, 20 and 21 illustrate three individual layers of rigidpolyurethane foam, applied and formed in succession. To secure evendistribution they are poured-in-place in subsequent increments, each onecoating the inner surface of the available inner cavity while the shellis being rotated and the foam forming composition is still liquid. 19coats the inner surface of the shell. 20 coats the inner surface of 19and 21 coats the inner surface of 20. In some cases it is advantageousto complete the distribution of the foam forming composition on theinterior surface of the cavity prior to commencement of the foaming. Theindividual layers of the solid polyurethane foam have good adhesion toeach other. The embodiment illustrated by FIG. 8 reduces the quantity ofpolyurethane foam utilized, reduces shrinkage and, by reducing thepressure during the foam expansion, eliminates the need for an outsidemold during the foaming operation in the majority of the cases. In oneembodiment of this invention, as illustrated by FIG. 8, 19 is a foam ofabout 20 to 25 p.c.f. and 20 and 21 are of a foam of about 2 to 3 p.c.f.The high density foam performs the main task of rigidification andprevents distortion during the second and third foaming step without theuse of a mold during foaming. In another embodiment all three layers of19, 20 and 2.1 are of a foam of about 1 /2 to 3 p.c.f. In FIG. 8 theouter shell component and the inner rigidifier component jointly form acavity.

FIG. 9 is an alternative form of FIG. 8. The additional feature is 22,illustrating an ancillary reinforcing element on the interior surface ofthe cavity formed jointly by the outer shell component and the threelayers of the inner rigidifying component. In this instance theancillary reinforcing element is advantageously either a flexible epoxyresin composition or a flexible polyester composition. They can beapplied by slush casting or rotational casting or by spray application.They are of a composition which cures either at room temperature or atlow elevated temperatures.

FIG. 10 is a front view of a three-dimensional illustration of acomposite article of manufacture of this invention, having both verticaland horizontal rectangular cross-sections. This type of object has agreater tendency to push outward during foaming as a consequence of thefoam rise. 19, 19-a, 19-b, 20, 20-a. 2042, 21, 21-a and 21-1) illustrate9 individual layers of rigid polyurethane foam, prepared as described inconnection with FIG. 8 in successive foaming steps. This layer methodeliminates the excessive pressure during foaming and simultaneously mayeliminate the need for an outer protective mold during the foaming.

FIG. 11 is a vertical cross-sectional view of a composite article ofmanufacture according to this invention. 14 is the molded shell. 23 is atube placed into the internal cavity of the molded shell. This tube canbe made e.g. of thin aluminum metal, or of chipboard paper or the like.The rigid polyurethane foam 15 is formed around the tubing. The effectis to reduce the inward shrinkage of the foam layer and also to reducethe quantity of polyurethane foam used.

FIG. 12-A and FIG. l2-B illustrate alternatives. They are verticalcross-sectional views of related and alternati=ve composite articles ofmanufacture of this invention. 14 is a molded plastisol shell. 24 is athin layer of molded plastics skin protruding into the internal cavityof the molded shell 14. During the foaming operation this thin layer of24 can be supported by a plug 25 which is then withdrawn after thefoaming operation is completed. 15-a is a rigid polyurethane foam whichhas been prepared by foaming around the plastic coated plug. The foam15a. fills out the space between the said plastics coated plug and themolded outer shell component. After the foaming producing 15-a iscompleted, according to the alternative illustrated by FIG. l2-A, theplug is removed, leaving the thin layer of plastics skin 24 as a coatingon the interior of the cavity of the foam layer 15-a. This illustratesthe utility for insulated containers, like thermos bottles. In anotheralternative, illustrated by FIG. l2-B, both the plastics skin 24 and theplug 25 of FIG. l2-A are withdrawn and the space obtained by suchwithdrawal is filled with a second quantity of rigid polyurethane foam15-b. This second quantity of foam 15-b is supported by the outer foamlayer of 1Sa during the foaming operation. In this last mentionedembodiment, illustrated by FIG. 12-B, 15a may be of a rigid higherdensity polyurethane foam with p.c.f. values of from about 20 to about25, whereas 15-b may have a p.c.f. value of from about 1 /2 to about 3.The high density foam performs the main task of rigidification andprevents distortion in the second foaming step without the use of amold.

The drawings illustrate some aspects of this invention and do not limitthe scope of the invention herein claimed.

I claim:

1. The process of producing a rigid impact resistant composite articleof manufacture comprising a hollow outer shell component which has anaccess opening to its cavity and a cellular inner rigidifier component,said process comprising the steps of (a) molding from a flexible pliableresilient organic plastics material a unitary substantially void-freehollow single shell component in a hollow mold, said shell componenthaving an access opening to its cavity, said molding step being carriedout to its completion to produce the shell component molded to its finalphysical strength and texturally decorative characteristics, said shellcomponent having the characteristics that it can be deformed at leasttemporarily by the application of hand pressure, while free of contactwith the rigidifier component, said organic plastics material comprisinga member of the class consisting of (i) vinyl chloride in a polymerizedand plasticized state, (ii) vinyl chloride and a reactive acrylicmonomer in a polymerized and plasticized state, (iii) ethylene in apolymerized state, (iv) propylene in a polymerized state, (v) ethyleneand vinyl acetate in a copolymerized state, (vi) ethylene andethylacrylate in a copolymerized state, (vii) polyallomers, (viii)natural rubber, (ix) methylmethacrylate in a polymerized state, (X)polycarbonates, (xi) flexible epoxy resins in a polymerized state, (xii)flexible polyesters in a polymerized state, (xiii) isocyanateelastomers, (xiv) ethyl cellulose, (xv) cellulose acetate, and (xvi)cellulose acetobutyrate, said shell component having at least oneundercut,

(b) removing the molded shell component from its mold,

(c) preparing in a separate step a liquid organic plastics compositioncapable of forming a rigid cellular structure in situ in the cavity ofthe premolded shell component obtained in step (a), said rigid cellularstructure when formed and set being a rigid foam comprising a member ofthe class consisting of (l) rigid polyurethane foams, (2) rigid epoxyfoams, (3) rigid polyvinyl chloride resin foams, (4) rigid phenolicresin foams, (5) rigid urea-formaldehyde foams, (6) rigid polyesterfoams, (7) asphalt foams, (8) hard rubber foams, (9) rigid siliconefoams, (10) rigid acrylic foams prepared from alphachloroacrylic acidester polymers and (11) rigid syntactic foams,

(d) introducing said liquid organic plastics composition prepared instep (c) into the cavity of the premolded shell component through itsaccess opening,

(e) causing said liquid organic plastics composition to foam-in-placeinside the cavity of said shell component obtained in step (a) after ithas been removed from its mold in step (b),

(f) solidifying the cellular structure so formed, and

(g) recovering the rigid composite article of manufacture so produced,said steps (d), (e) and (f) carried out in a manner to deposit a rigidfoam in intimate contact with the entire inner surface of the hollowouter shell component, said deposit having a wall thickness of at leastone-half of the wall thickness of the outer shell component and beingsutficient to prevent the deformation of the shell component by handpressure, thereby rigidifying the hollow shell component in itsentirety.

2. The proces of claim 1, wherein the liquid organic plasticscomposition in step (d) is poured into the cavity of the hollow shellcomponent.

3. The process of claim 1, wherein a layer of adhesive is applied to theinner surface of the outer shell component prior to introducing theliquid organic plastics composition forming the rigid cellular structureinto the cavity formed by said outer shell component, said adhesivehaving good adhesion both to the plastics of which the outer shell ismolded and to the rigid foam of the inner rigidifier component.

4. The process of claim 1, wherein the outer shell component is in amulti-piece mold during the formation of the inner rigidifier component.

5. The process of claim I, wherein in step (d) the introducing of theliquid organic plastics composition into the cavity of the premoldedshell component through its access opening is carried out by spraying.

6. The process of producing a rigid impact resistant composite articleof manufacture comprising a hollow outer shell component which has anaccess opening to its cavity and a cellular inner rigidifier component,said process comprising the steps of (a) molding from a flexible pliableresilient organic plastics material a unitary substantially void-freehollow single shell component in a hollow mold, said molding steps beingcarried out to its completion to produce the shell component molded toits final physical strength and texturally decorative characteristicsand in a manner to yield an outer shell component with a wall thicknessfrom about 15.5 mils to about 250 mils, said shell component having thecharacteristic that it can be deformed at least temporarily by theapplication of hand pressure, while free of contact with the rigidifiercomponent, said organic plastics material comprising a member of theclass consisting of (i) vinyl chloride in a polymerized and plasticizedstate, (ii) vinyl chloride and a reactive acrylic monomer in apolymerized and plasticized state, (iii) ethylene in a polymerizedstate, (iv) propylene in a polymerized state, (v) ethylene and vinylacetate in a copolymerized state, (vi) ethylene and ethylacrylate in acopolymerized state, (vii) polyallomers, (viii) natural rubber, (ix)methylmethacrylate in a polymerized state, (x) polycarbonates, (xi)flexible epoxy resins in a polymerized state, (xii) flexible polyestersin a polymerized state, (xiii) isocyanate elastomers, (xiv) ethylcellulose, (xv) cellulose acetate, and (xvi) cellulose acetobutyrate,said shell component having at least one undercut,

(b) removing the molded shell component from its mold,

(c) preparing in a separate step a liquid organic plastics compositioncapable of forming a rigid cellular structure in situ in the cavity ofthe premolded shell component obtained in step (a), said rigid cellularstructure when formed and set being a rigid foam comprising a member ofthe class consisting of (1) rigid polyurethane foams, (2) rigid epoxyfoams, (3) polyvinyl chloride resin rigid foams, (4) rigid phenolicresin foams, (5) rigid urea-formaldehyde foams, (6) rigid polyesterfoams, (7) asphalt foams, (8) hard rubber foams, (9) rigid siliconefoams, (10) rigid acrylic foams prepared from alpha-chloroacrylic acidester polymers, and (11) rigid syntactic foams,

(d) introducing said liquid organic plastics composition prepared instep (c) into the cavity of the premolded shell component through itsaccess Opening,

(e) causing said liquid organic plastics composition to foam-in-placeinside the cavity of said shell component obtained in step (a) after ithas been removed from its mold in step (b),

(f) solidifying the cellular structure so formed, and

(g) recovering the rigid composite articles of manufacture so produced,said steps ((1), (e) and (f) carried out in a manner to deposit a rigidfoam in intimate contact with the entire inner surface of the hollowouter shell component, said deposit having a wall thickness of at leastone-half of the wall thickness of the outer shell component and beingsufficient to prevent the deformation of the shell component by handpressure, thereby rigidifying the hollow shell component in itsentirety.

7. The process of claim 6, wherein the liquid organic plasticscomposition prepared in step (c) is a prepolymer composition yielding arigid polyurethane foam structure.

8. The process of claim 6, wherein the liquid organic plasticscomposition prepared in step (c) is a quasi-prepolymer compositionyielding a rigid polyurethane foam structure.

9. The process of claim 6, wherein steps (c), (d), (e), and (f) arecarried out in a way to bring about filling of the cavity of the outershell component with the rigid cellular structure in its entirety.

10. The process of claim 6, wherein step (d) is carried out by castingand steps (d), (e), and (f) bring about the lining of the inner surfaceof the outer shell component with a layer of the rigidifier component,thereby jointly forming a cavity of the shell component and therigidifier component, said rigidifier component being in intimatecontact with the entire inner surface of the outer shell component.

11. The process of claim 6, wherein steps (d), (e), and (f) bring aboutthe lining of the inner surface of the outer shell component with alayer of the rigidifier component, thereby jointly forming a cavity ofthe shell component and the rigidifier component, said rigidifiercomponent being in intimate contact with the entire inner surface of theouter shell component and, in an additional step, dcpositing a roomtemperature setting resinous composition on .the inner surface of saidjoint cavity, said resinous composition being a member of the classconsisting of room temperature setting flexible epoxy resins and roomtemperature setting flexible polyester resins and setting the castresinous composition.

12. The process of claim 6, wherein steps (c), (d), (e), and (f) arecarried out by slush casting in a way to bring about the lining of theinner surface of the outer shell component with a layer of therigidifier component, thereby jointly forming a cavity of the shellcomponent and the rigidifier component, said rigidifier component beingin intimate contact with the entire inner surface of the outer shellcomponent.

13. The process of claim 6, wherein steps (0), (d), (e), and (f) arecarried out by rotational casting in a way to bring about the lining ofthe inner surface of the outer shell component with a layer of therigidifier component, thereby jointly forming a cavity of the shellcomponent and the rigidifier component, said rigidifier 30 componentbeing in intimate contact with the entire inner surface of the outershell component.

14. The process of claim 6, wherein steps (c), (d), (e), and (f), arecarried out in a way to bring about the incremental lining of the innersurface of the outer shell component with successive layers of therigidifier component, the first layer of said rigidifier component beingin intimate contact with the entire inner surface of the outer shellcomponent.

15. The process of claim 6, wherein steps ((1), and (e) are carried outin the premolded shell component per se, while the latter is free of thesupport of a reinforcing mold, and said steps (d), (e), and (f) arecarried out at ambient temperatures.

16. The process of claim 6, wherein steps (c), (d), (e), and (f) arecarried out in a manner to form successive horizontal layers inside saidcavity.

17. The process of producing a rigid impact resistant composite articleof manufacture comprising a hollow flexible pliable and resilient singleouter shell component which has an access opening to its cavity and acellular inner rigidifier component, said process comprising thesequence of the steps of (a) casting plastisol in a hollow seamless die,

(b)heating the plastisol to gelation temperature,

(c) fusing the gelled plastisol layer to form a tough and substantiallyvoidfree premolded outer shell component, said fusion step being carriedout to completion to produce the shell molded to its final physicalstrength and texturally decorative characteristics,

(d) stripping the premolded shell component from the die which providedat least one undercut,

(e) preparing in a separate step a liquid organic plastics compositioncapable of forming a rigid cellular struc ture in situ in the cavity ofthe premolded shell component obtained in steps (a) to (d), said rigidcellular structure when formed and set being a rigid foam comprising amember of the class consisting of (l) rigid polyurethane foams, (2)rigid epoxy foams, (3) rigid polyvinyl chloride resin foams, (4) rigidphenolic resin foams, (5) rigid ureaformaldehyde foams, (6) rigidpolyester foams, (7) asphalt foams, (8) hard ruber foams, (9) rigidsilicone foams, (10) rigid acrylic foams prepared fromalpha-chloroacrylic acid ester polymers and (11) rigid syntactic foams,

(f) introducing said foam forming liquid organic plastics compositioninto the cavity of the premolded shell component through its accessopening,

(g) causing said liquid organic plastics composition to foam-in-placeinside the cavity of said shell component obtained in steps (a) to (c)after it has been removed from its mold in step (d),

(h) solidifying the cellular structure so formed while providing thecellular rigidifier component to be in intimate contact with the entireinner surface of the outer shell component, and

(i) recovering the rigid composite article of manufacture so produced,

said steps (f), (g) and (h) carried out in a manner to deposit a rigidfoam in intimate contact with the entire inner surface of the hollowouter shell component, the wall thickness of said deposit beingsufficient to prevent the deformation of the shell component by handpressure, thereby rigidifying the hollow shell component in itsentirety, said plastisol being a dispersion of a polyvinyl resin inliquid organic plasticizers and said polyvinyl resin comprising vinylchloride in a polymerized state.

18. The process of claim 17, wherein the outer shell component formed bysteps (a), (b) and (c) has a wall thickness of from about 15.5 mils toabout 250 mils.

19. The process of claim 17, wherein the plastisol outer shell componentis prepared by slush casting and any excess of plastisol is poured olfprior to the fusion step (c).

2.0. The process of claim 17, wherein the plastisol outer shellcomponent is prepared by rotational casting.

21. The process of producing a rigid impact resistant composite articleof manufacture comprising a hollow outer shell component which has anaccess opening to its cavity and a cellular inner rigidifier component,said process comprising the steps of (a) molding from a flexible pliableresilient organic plastics material a unitary substantially void-freehollow single shell component in a hollow mold, said molding step beingcarried out to its completion to produce the shell component molded toits final physical strength and texturally decorative characteristicsand in a manner to yield an outer shell component with a wall thicknessfrom about 15.5 mils to about 250 mils, said shell component having thecharacteristic that it can be deformed at least temporarily by theapplication of hand pressure, while free of contact with the rigidifiercomponent, said organic plastics material comprising a member of theclass COnsisting of (i) vinyl chloride in a polymerized and plasticizedstate, (ii) vinyl chloride and a reactive acrylic monomer in apolymerized and plasticized state, (iii) ethylene in a polymerizedstate, (iv) propylene in a polymerized state, (v) ethylene and vinylacetate in a copolymerized state, (vi) ethylene and ethylacrylate in acopolymerized state, (vii) polyallomers, (viii) natural rubber, (ix)methylmethacrylate in a polymerized state, (x) polycarbonates, (xi)flexible epoxy resins in a polymerized state, (xii) flexible polyestersin a polymerized state, (xiii) isocyanate elastomers, (xiv) ethylcellulose, (xv) cellulose acetate, and (xvi) cellulose acetobutyrate,said shell component having at least one undercut,

(b) removing the molded shell component from its mold,

(c) preparing, in a separate step, a polystyrene composition suitable toform a rigid cellular structure in situ in the premolded shellcomponent,

(d) introducing said polystyrene composition into the cavity of thepremolded shell component through its access opening while the shell isin a supporting mold,

(e) causing the polystyrene composition to foam-inplace inside thecavity of the shell component,

(f) solidifying the cellular structure so formed, and

(g) recovering the rigid composite article of manufacture so produced,

said steps ((1), (e) and (f) providing the cellular rigidifier componentto be in intimate contact with the entire inner surface of the outershell component, thereby rigidifying the hollow shell component in itsentirety and preventing the deformation of the shell component by handpressure.

References Cited UNITED STATES PATENTS 1,998,897 4/1935 Kay 264310 X2,753,642 7/1956 Sullivan 264- X 2,787,809 4/1957 Stastny 264532,880,467 4/1959 Wibbens 26445 2,950,505 8/1960 Frank 26445 2,974,3733/1961 Streed 26445 3,091,946 6/1963 Kesling 26445 X 3,133,853 5/1964Knox 26445 X 3,163,686 12/1964 Dusel 26445 3,198,864 8/1965 Bingham264250 3,283,386 11/1966 Cenegy 26445 DONALD J. ARNOLD, Primary ExaminerP. A. LEIPOLD, Assistant Examiner U.S. Cl. X.R.

